Can anyone help?

[+benp1]

I recently bought a 2nd hand Garmin Etrex Vista C on ebay. Great condition etc etc

 

I went out on the weekend to find my first geocache and had no luck whatsoever. I went to find this one - http://stats.guk2.com/caches/osgb_cache_de...s.php?wp=GCWCR9

 

Its nice and local, is big and looked relatively easy. When I got there I couldn't get a good lock on the gpsr. I can't remember exact details but I think I had about 3/4 satellites locked, if not more. The accuracy at best was +/- 21ft. I was completely out in the open and it was a very clear day. I knew I was close because I drove to a place to park very close (looking at a map). When I got there the circle on the map on the gpsr showing its accuracy was way outside where i was and the cache itself. There was no way I could find it, it just wasn't accurate enough.

 

I was disappointed to say the least. I was expecting much more.

 

From what I could see the WAAS on the unit was enabled. I'm not sure if that helps or not. It just wouldn't get anymore accurate

 

I walked around a bit and even went in the woods to see if it changed. It did - +/- 40 odd ft

 

can anyone help? Does anyone know why this happened?

[Nediam]

Hi Benp1 and welcome to Geocaching and the forums

 

Do you know if the GPSr is set to the correct datum? i.e. WSG84

 

Unfortunately I don't have a Garmin Etrex Vista C so can't help you with the specifics on that handset - but I'm sure somone will be along soon who can help

 

Hve you tried looking at the pinned topics at the top of the UK forum page? There may be something there that can help.

Edited December 20, 2006 by Nediam

[+HazelS]

Well done on getting your 1st GPS and getting out there....

 

The GPS will very rarely take you to the exact position of the cache, and to be honest, for my 1st several, I used ot clue before I set off.

 

Once you've done some caches you'll discover your "cachers eye" where you can walk to within 30 ft of the cache and instantly know where it'll be placed because experience counts for a lot!

 

If you're out in the open then you needn't have WAAS on...as far as I know (and I'm not a technical person) it averages your position, so for no tree cover it's not necessary.

 

Other than that - once I got to within about 25 - 30ft of the cache, I'd just start hunting without the GPS and think "If I were going to hide something, where would I hide it?" Use the clue....

 

Hope that helps - and Good luck!!

[+PopUpPirate]

Looking at that cache page, and reading the latest logs, it mightve been out of action when you went hunting

[+webscouter.]

If you didn't let the gps spend at least 30 minutes with a satelite lock you might not have the correct almanac downloaded. The gps satelites send data as to where they are at, corrections etc. If your unit came from a long way away and hasn't been used for a long time the almanac may have changed slightly. Because timing is so critical even a little time/position of satelite error can make a large difference on your end.

 

Set your new gps on the back porch for thirty minutes or so and see if that doesn't help.

 

As far as WAAS goes, they are stationary satelites that recieve a signal from a ground station. Because they know where they are they will see the same deviation coming from the ground as what the ground reciever will see coming from the satelite. This deviation is caused by atmosphere, sun activity etc. They can then transmit this error correction to your gps which will then adjust your position.

[+dysdera]

Dont get disillusioned, I have not been able to find many caches. Tree cover is a nightmare, and although I have not done this cache, it looks as if it has some.

Having looked on Groundspeak, There is a cache very near you which I have done called 'North of London Travel Bug Hotel' which is easy in all respects and being a travel bug hotel should have a few of them in.

sometimes the gps will only get you a reasonable distance from the cache, as you may have to factor in errors by the placer, so don't assume that you are at fault, as I have found many where the co-ordinates are way out.

Hope this is of some help, and last of all.....WELCOME!!

[+benp1]

Thank you all for your (very quick) replies

 

I didn't know about the WGS84 datum thing, i'll have a look tonight when I get home.

 

I picked this one as from what I could see on the description, it was a fairly large box and fairly easy. I know the place a bit so knew roughy where I should be looking. But when I got there it was SO inaccurate that I really didn't know where it would be. The wood is pretty small but being so new to the game I wouldn't have a clue where it might be. I went for a little wonder around the wood to see if I could spot anything but didn't have any luck. I was hoping the gpsr might take me to a rough spot but it was more of a rough area

 

I'll try leaving it out in the same place for a while to see if it helps.

 

My problem is that because it was first time i didn't really know what i was looking for. And being in a wood there are lots of places to hide things!

 

Thank you also for being so helpful and welcoming me!

Edited December 20, 2006 by benp1

[+Dorsetgal & GeoDog]

Welcome Benp1, both to geocacing and the forum! It may well be the datum thingy, so let us know how it goes when you get gpsr back in hand!

 

One thing that I have found very useful, and I didn't use it until I had found about 200 caches (mainly cos my pc wasn't up to it) is Google earth. You can put the co-ordinates into it and it will show you the general area. You can also click on the map links on the cache page; I prefer the Streetmap one, but others have different preferences.

 

Good luck; oh and a word of warning; this game / sport / passtime / hobby is highly addictive and there is no known cure!

[+2202]

It is also possible, that due to satelite alignement, ie in line and all in the quadrant overhead, that decent triangulation cannot be achieved and accuracy goes out the window.

However at 21ft I would be more than happy with that. An occasion recently with total veiw of the sky in the middle of the field, due to the juxstapostion of the satelites, I was getting only a 15metre (so called) accuracy......till found it though.

Such is caching life!

[+PopUpPirate]

Moorland caches are much easier - even I can find them

[+The Cache Hoppers]

Ben there is a spoiler pic showing the cache hide on that cache listing which should help. I agree with PopUpPirate though ... it may very well be out of action. Have you tried emailing the cache owner to find out?

 

You might like to register as a newbie on the Adopt A Newbie pinned thread on the forums and go out with someone who has a few caches under the belt to get your cacher's eye tuned in. Welcome to geocaching and the forums, Liane.

Edited December 20, 2006 by The Cache Hoppers

[+benp1]

Liane, thank you for the spoiler picture. I clicked on that when I was looking at the description but the picture came up very small and I didn't venture any further. How did you manage to get the picture so large. I'm guessing (from your link) that you didn't save it to your computer and then zoom in. Had I seen that picture beforehand I might have had more of a chance

 

I was disappointed at 21ft accuracy; I thought it would be more accurate. I guess that if I knew more about the cache itself I might have tried to look in the vicinity and see if I could see it.

 

One thing that I do remember about the gpsr when I was looking for it. The circle which sits on the map indicating how accurate it is (well, this is my understanding) seemed very large, larger than 21ft on the map (even taking into account the scale). Is there something else I haven't done? When I think about it now it wouldn't seem like an accuracy of 21ft.

 

I've just checked my unit and it's definitely set to WGS84. I guess I have to leave it out and let it get a lock. The only problem is that I don't have a garden (i'm in a flat).....

 

Are you guys honestly able to find a cache from the description if you were plonked in the right area? As in directed there by your gps. I really appreciate the advice in registering and getting someone experienced to show me the ropes, but i'd really like to see if i can work it out on my own first - that would be my last resort! It seems like its going to be good fun, just need to find a cache first!

[+The Forester]

One thing that I do remember about the gpsr when I was looking for it. The circle which sits on the map indicating how accurate it is (well, this is my understanding) seemed very large, larger than 21ft on the map (even taking into account the scale). Is there something else I haven't done? When I think about it now it wouldn't seem like an accuracy of 21ft.

 

This "accuracy" is a misnomer which causes a lot of confusion.

 

"Accuracy" is defined as the degree of closeness to the true value. Your GPSr does not know the true value, or else it would surely tell you the true value instead of whatever it is telling you is its position, so it cannot possibly know its "accuracy".

 

To gain some confidence in your GPSr, try a little experiment. Look up the coordinates of a suitable triangulation pillar on the Ordnance Survey website. Use the Lat/Long, not the grid co-ordinates. Create a waypoint in your GPSr with these co-ords and plonk the machine on the pillar. Watch the distance readout on the screen. Now that really is an indication of the accuracy of the machine.

[+John Stead]

I would not be too disappointed at only getting 21ft accuracy and you should bear in mind that that is only what the GPSr thinks its accuracy to be - it may be more or less and also the original setter may not have the coordinates absolutely accurate. So there are a lot of variables to play with. If you go again you may be lucky and get taken straight to it but as has been suggested perhaps you might check with the owner that it is still in place. If you had logged your visit as a DNF (Did Not Find) the owner would get a message that you had not found it and might go and check, if two of three cachers logged DNFs then the reviewers might suggest to him that he should do something or archive it. That is why it helps everyone if you have had a serious try to find a cache and been unable to do so. As it is I see that it has been marked as needing maintenance.

Anyway good luck with your next cache, and the next one after that, and the next one after that, and the next one after that . . . you have been warned that it is addictive - but great fun.

[+drsolly]

We've only been caching for three months, so I still remember the difference between then and now.

 

Firstly, 21 feet accuracy isn't too bad. I usually reckon that when I'm within 15 feet of the zero point, that's about it. If it tells me 10 feet, then I reckon that's as good as I'm going to get.

 

Here's some of the stuff I think I've learned.

 

The more satellites your GPSr has picked up, the better the accuracy will be.

 

Don't forget that the person setting the cache, also has an equally inaccurate GPSr. So, the 20 feet accuracy of your GPSr, has to be added to the 20 feet accuracy of their GPSr,, so that's a total of 30 feet or so (root of sum of squares).

 

If you stand still while at what you think is the ground zero point, the GPSr will wander around a bit. That gives you some idea of the inaccuracy

 

Read the wilkipedia on this:

 

http://en.wikipedia.org/wiki/Global_Positi...d_Error_Sources

 

Trees act as signal reflectors and blockers. Leaves act as signal blockers. When the signal is blocked, you'd get fewer satellites in your lock (i.e. less accuracy) or even no lock at all. When your get signal reflection, that fools the GPSr about where it is. This is usually slight (some feet), but I once had it half a mile out.

 

You can get a GPS antenna. I'm still trying to see how much use that is.

 

WAAS is supposed to improved accuracy, quite a lot. But you need to get data from a WAAS satellite, and I'm a bit confused about whether that's currently available in Europe (where it's called EGNOS). Maybe the accuracy I'm seeing now is inclusive of the EGNOS? It's hard for me to see if that's right.

 

Do other folks have better info that my list above?

[+The Forester]

data from a WAAS satellite, and I'm a bit confused about whether that's currently available in Europe (where it's called EGNOS)

 

It is available in Europe and has been for several years. The accuracy of a WAAS/EGNOS-assisted fix is almost always better than the claimed ±3m accuracy.

 

As with anyy GPS fixes, you can greatly improve the quality of a fix by averaging lots of fixes. The more the better, usually.

[+scottpa100]

data from a WAAS satellite, and I'm a bit confused about whether that's currently available in Europe (where it's called EGNOS)

 

It is available in Europe and has been for several years.

I have a GPSmap60CS which does have WAAS capability. I have always switched it off in the past as I thought WAAS was just a north American thing and therefore would waste battery power. Then I found out about EGNOS! The WAAS capability was switched back on, and where I am on the central north Wales coast, I don't get any WAAS/EGNOS reception. Is the WAAS/EGNOS only a continental Europe thing and perhaps can only be picked up by peeps on the eastern side of the country?

[+scottpa100]

Don't forget that the person setting the cache, also has an equally inaccurate GPSr. So, the 20 feet accuracy of your GPSr, has to be added to the 20 feet accuracy of their GPSr,, so that's a total of 30 feet or so (root of sum of squares).

 

 

I think what is mentioned above is really important. Whenever I'm out caching with my Dad and he goes on one (bless him) about "These co-ordinates aren't right, look how far we are from over there to where we've actually found the cache" and I'll quite often go what's our accuracy "+-10m" so if the other person was +-10m, then the possible search area is huge!

[+Phil and Ruth]

I've just checked my unit and it's definitely set to WGS84. I guess I have to leave it out and let it get a lock. The only problem is that I don't have a garden (i'm in a flat).....

 

Do you have a south*-facing Window? If so, try placing the GPS on the window sill - we live in a flat and can get a lock indoors this way.

 

* South is better (I think) because there are more satelites for your unit to "see" in that direction.

[+MartyBartfast]

Benp1, your first caching experience sounds pretty much like mine. Our first attempt was a cache in the trees, we spent a good while tramping round with no joy so we gave up, we tried a couple on more open land a few days later and got them with no trouble so headed back to the first and got it almost straight away, we must have walked over it 4 or 5 times on the first trip and missed it.

 

BTW I never get better than 5m 'accuracy' from my Etrex banana, but anything under 10m is usually enough.

[+scottpa100]

Is the WAAS/EGNOS only a continental Europe thing and perhaps can only be picked up by peeps on the eastern side of the country?

 

I've answered my own question. Maps of WAAS and EGNOS coverage available here.

 

WAAS and EGNOS coverage

[+DutchGeek & Lollypops]

 

One thing that I do remember about the gpsr when I was looking for it. The circle which sits on the map indicating how accurate it is (well, this is my understanding) seemed very large, larger than 21ft on the map (even taking into account the scale). Is there something else I haven't done? When I think about it now it wouldn't seem like an accuracy of 21ft.

 

 

Don't worry too much about the blue circle either. The blue circle size depends on the "accuracy" of the map you are navigating across, which I presume is the basemap on your GPS. With my 60Cx, I will get a fairly small circle if I'm zoomed right in on my mapsource maps, but if I then zoom right out until the indicator in the bottom LH corner says basemap, the circle suddenly becomes huge because the base map on my unit is pathetic anywhere outside the US (it came from America and has US basemap loaded). You are nearly always safer using the arrow screen to find a cache, when I get to within 10-15 feet of the waypoint, I then start searching.

[+clotguy]

I too am new at this but what you need ( and will get quickly) is cachers eye, that uncanny ability to get as close as your GPS will allow (3m is the best I ever get) and 'know' where the hidding place is.

At first I couldn't find anything without the help of my 7 year old who must have been born with the eye, but now I 'see' and caching has become a little easier

Edited December 21, 2006 by clotguy

[+t.a.folk]

Been at it ages and I still don't even use "go to "facility.

When the numbers are the same as those on cache sheet I'm more or less there ,whereas husband using" go to" has walked on past !

Don't think either of us use the accuracy facilty .

Open area an clear sky usually ='s good co-ords .

If there are trees or tall buildings we find our g.ps.'s often can't make up their minds where they are and prefer to dance and lead us a merry one . All part of the fun !

[Edgemaster]

To gain some confidence in your GPSr, try a little experiment. Look up the coordinates of a suitable triangulation pillar on the Ordnance Survey website. Use the Lat/Long, not the grid co-ordinates. Create a waypoint in your GPSr with these co-ords and plonk the machine on the pillar. Watch the distance readout on the screen. Now that really is an indication of the accuracy of the machine.

 

There's not many real pillars in London still in the passive trigpoint database, and the historical database doesn't give lat/long.

 

TrigpointingUK has an easier to use search, benp, the nearest to the above cache is Arkley Resr which is a nice real pillar, which is so unlike London!

(This is at N51 38.872 W000 14.206)

 

Note: Both TrigpointingUK and GeocacheUK are suffering from christmas party sickness, they may come back sometime soon, hopefully.

Edited December 21, 2006 by Edgemaster

[+drsolly]

Is the WAAS/EGNOS only a continental Europe thing and perhaps can only be picked up by peeps on the eastern side of the country?

 

I've answered my own question. Maps of WAAS and EGNOS coverage available here.

 

WAAS and EGNOS coverage

 

That article is dated Feb 2006. It says:

 

"EGNOS is broadcasting a "do not use" indication. So it is unlikely that users in Europe will see any response from EGNOS until" ...

 

 

So you can see why I'm still confused about whether we're getting the benefit of EGNOS at this date. Is there a way we can interrogate our GPSrs to see if they're using WAAS/EGNOS?

[+John Stead]

Is there a way we can interrogate our GPSrs to see if they're using WAAS/EGNOS?

 

I do not know about other GPSrs, but both my Garmins on the screen showing the constellation of satellites come up with satellites numbered over 30 if WAAS is switched on in the instrument and shows a D against each of the satellites whose signals are being corrected.

Edited December 21, 2006 by John Stead

[+Happy Humphrey]

I do not know about other GPSrs, but both my Garmins on the screen showing the constellation of satellites come up with satellites numbered over 30 if WAAS is switched on in the instrument and shows a D against each of the satellites whose signals are being corrected.

Mine does the same, and indicates "2D DIFF" as well. I've seen this a lot lately: it was receiving EGNOS most of the time on Monday (switched on for about 6 hours). It was pretty much inch perfect on the caches I looked for.

 

Back on the main topic, 21 feet is not at all disappointing and should be fine for caching. I'd be happy to search for a large box within seven paces. I regard the figure as a level of confidence, i.e. 100 feet means that the calculated position is the best guess but is likely to be anything up to 100 feet out. Normally, if it's showing 21 feet then you will probably get taken right up to the cache position.

 

But the first posting slightly confuses me. Normally, I'd follow the "arrow" on the GPSr until the screen says I'm a few feet from the cache, and then start looking. You seem to be saying that you were just watching the map, and with no mention of the indicated distance from the waypoint I suspect that you weren't using the arrow at all. I don't know what the map page looks like on your GPSr, but I expect that the technique of trying to match your position on the map with the waypoint will result in caching misery! Did you check the other pages on your GPSr?

 

HH

[+benp1]

Sorry for the taking so long to reply. Thank you all for your help and posts.

 

I went out today to find another cache (http://stats.guk2.com/caches/osgb_cache_details.php?wp=GCMGXQ) but again had no luck. I'm kinda happy with the accuracy of the gpsr now, at least this is common amongst all of you.

 

I've posted in the adopt-a-newbie thread so I hope to have some help soon. Thanks again

[+MartyBartfast]

I see from your post in "Adopt a newbie" that you're in Finchley, you might like to check out this thread where people were recently discussing a get together for North London cachers, maybe you could tag along.

[+kevenh]

EGNOS is turned on ( http://www.pocketgpsworld.com/egnos.php )

 

The "do not use" indication embedded in the signal seems to be mandatory until the testing is finished.

[+sssss]

benp1 i am also available to lend a hand if you need